Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

In Band Fallback Mechanism for Inverse Multiplexers

IP.com Disclosure Number: IPCOM000118705D
Original Publication Date: 1997-May-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 108K

Publishing Venue

IBM

Related People

Beam, AD: AUTHOR [+2]

Abstract

An N-channel coherent transmission system is one in which N independently transported signals (such as N T1 signals) are caused to be cohered into a single channel of N times the single channel bit rate. As such, the system is susceptible to independent failure of one or more of the N constituent signals, and their later restoral. The system must operate such that upon loss of one of the constituent signals, the link does not simply go down, but rather that it be reconfigured to support a bit rate of N-1 times the single channel rate, rather than the normal N times. When the failed constituent signal is restored, the system must then revert back to its full N times bit rate.

This text was extracted from an ASCII text file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

In Band Fallback Mechanism for Inverse Multiplexers

      An N-channel coherent transmission system is one in which N
independently transported signals (such as

N T1

signals) are caused
to be cohered into a single channel of N times the single channel bit
rate.  As such, the system is susceptible to independent failure of
one or more of the N constituent signals, and their later restoral.
The system must operate such that upon loss of one of the constituent
signals, the link does not simply go down, but rather that it be
reconfigured to support a bit rate of N-1 times the single channel
rate, rather than the normal N times.  When the failed constituent
signal is  restored, the system must then revert back to its full N
times bit rate.

      Present T1 inverse multiplexers with eight integrated T1 Data
Service Unit/Channel Service Unit (DSU/CSU) channels convert a
digital data stream with a data rate up to 12.2 Mbps from a Data
Terminal Equipment (DTE) source into multiple DS1 formatted channels
for transmission via T1 circuits.  At the other end of the T1 network
spans, the data from all T1 circuits is reassembled into the original
high speed data stream.  Differential delay of up to 32 msec across
the T1 circuits can readily be accommodated in the T1 realignment at
the receiving end.

      The In-Band alignment technique for T1 inverse multiplexers
utilizes the first bit of the first DS0 channel of each T1 frame, for
alignment.  This same time slot (first DS0 of each frame) also is
utilized for in-band T1 line management, i.e., dropping a faulty line
from service ('fallback') and subsequently restoring the line.  As an
alignment control, a pseudo random (PN) sequence which repeats after
N frames are inserted into the first bit position of each frame
(after the frame bit).  This pattern will be searched out by the
mating inverse  multiplexer on the receiving end.  As long as the
differential path delay among all T1 circuits is less than one half
of the time for the PN  sequence to repeat, then the T1 lines can be
cohered at the receiving end, by finding the start of the PN sequence
in each of the T1 lines.  The depth of an elastic buffer at the
receiving end will determine the maximum differential delay allowed
between the T1 circuits.  After each T1 channel has acquired frame
sync to the PN sequence, a cohered set of T1 channels is available to
read out of the  First In/First Out (FIFO) buffers.

      T1 framers automatically monitor the status of each T1 channel
and signal the local processor if one or more of the T1 channels
should be dropped due to sub-standard performance, or the detection
of a major  alarm.  Any faulty or sub-standard T1 span will
'fallback' out of service  until it subsequently is observed to be
free from defect and can be restored to service.  When a 'fallback'
T1 line is taken out of service,  the remaining T1 lines are
realigned to carry the entire DTE data stream.  Since the...